1. Field of the Invention
The present invention relates to an ossicular prosthesis of the middle ear, of such a type as to replace at least partly the ossicular chain and to link a first organ or element, particularly the foot plate or the stirrup or stapes, with a second organ or element, particularly the hammer or malleus or the eardrum, which prosthesis can self-adjust by elasticity.
2. Brief Discussion of the Related Art
The middle ear has the task to convey the sound vibrations reaching the eardrum from an aerial environment to a watery environment, namely the inner ear, which constitutes a receiver element of perception of a sound wave.
The conduction of the latter is effected by an anatomic element, called the middle ear conductive system, constituted by a tympanic membrane adjoining an ossicular chain formed, from the outside to the inside, by the malleus, the anvil or incus and the stapes. The tympanic membrane adjoins this chain by the handle of the malleus. The stapes rests on a plate which on its internal base enters into contact with the watery environment, also called labyrinthine environment, of the inner ear.
The function of the ossicles of ossicular chain is to establish the contact between the eardrum and this labyrinthine environment, which constitutes the columellar effect. The ossicular eardrum system is suspended in the aerial cavity of the middle ear. Thus, there is no direct contact of this system with the osseous walls in order to convey acoustic energy originating from the tympanic membrane, namely the external ear, towards the inner ear.
The fixation point of the ossicular eardrum system are two annular ligaments situated at its extremities, namely that of the tympanic membrane and that of the foot plate.
The object of the present invention is to correct the conductive hearing loss, namely resulting from disorders on the ossicular chain after different pathologies.
The ossicular prosthesis for the middle ear have the purpose of replacing, at least partially, this ossicular chain, be it only the incus, the stapes and the incus, or also the stapes, the incus and the malleus.
Until now the available prosthesis are made out of various materials, such as a ceramic material, and consisting of a rod or shaft resting on the head of the stapes or on the foot plate, topped by a platform that makes contact with the handle of the malleus or on the eardrum. Because of the nature of the constructive material, these prostheses present an essentially rigid construction.
This solution presents a number of disadvantages. Thus, first of all, it is necessary that the surgeon has at his disposition a large number of prosthesis of different sizes and shapes, in order to be able to choose among them the most appropriate one for the implantation to be effected.
Furthermore, it is necessary to modify the size of these types of prosthesis, either by cutting them or by milling them so as to adapt their sizes to those of the "defects," namely of the elements missing from the ossicular chain. This brings about a modification of the condition of the surface of the prosthesis, which contributes to weaken it, to locally modify its interface, and constituting an attraction for an inflammatory reaction.
Lastly, in view of the fact that these prostheses are rigid and have dimensions that cannot be modified, their anchoring point on the elements which they are supposed to link consists of a simple contact, so that the prosthesis is placed only under a passive tension between these elements. This does not allow the reconstitution of a perfectly stable unit, even after an accurate placing of the prosthesis, which explains the many displacements that were observed after an operation. Thus, only about 75% of the partial prostheses, and 50% of the total ones, have shown to have a sufficient mechanical resistance.
In order to remedy these problems of stability, other middle ear prosthesis were suggested, in particular in WO-A-92/18066. This document describes a prosthesis constituted by two independent elements maintained in contact, of which one moves with respect to the other by means of a mechanical spring-system. Such adaptation provides a possibility of deformation of the prosthesis while being its installed. However, the mechanical stresses exercised by these prosthesis on the elements they link are not constant due to the fact of the frictional forces taking place between the two constituent elements of the prosthesis. This leads to a great risk of traumatism at the surfaces of the elements in contact with this prosthesis. Moreover, the latter presents a relatively complex mechanical structure which leads to a high cost, and wherein the functioning can be altered by the presence of tissues at the spring.